Currently, battles aren't very readable. There's a lot of difficult to find facts about performance that could be announced more prominently.

For example, if the user has been running around on the world map then gets in a battle, their Agility is decreased for the fight. This is only marked with a small icon, though. The icons are hard to see, and some of them aren't very clear.

It would be very useful if these statuses were announced with some kind of text. Perhaps 'Tired!' for Agility down on too much running. There's one that looks like dynamite; I still have no idea what it does =p

For example, if the user has been running around on the world map then gets in a battle, their Agility is decreased for the fight. This is only marked with a small icon, though. The icons are hard to see, and some of them aren't very clear.

Yep, all that needs a bit of documentation somehow. That's why it is planned to add a quick in-game doc with images. In the meanwhile, to at least give the player hints about what things do, I added those icons into the 'party' menu so that you can visually link the stats and their icon. The rest will come later.

It would be very useful if these statuses were announced with some kind of text. Perhaps 'Tired!' for Agility down on too much running. There's one that looks like dynamite; I still have no idea what it does =p

The text idea is IMHO a bad one. More text means more translation whereas I'm trying to push to the opposite effort. Replace more text with icons and explain them somehow. (That's why I replaced the game time and money texts with icons btw)

The "dynamite" one is not the best indeed. XD In fact, it's a wand meaning magical attack (See the party menu). Those icons come from Allacrost and most are actually good ones but if you've got meaningful replacement graphics with open license, we could work replacing those.

Also, it seems like some enemies are immune to some effects (Fenrir seemed immune to stun, for example). This should be noted! Floating text for 'Immune!' would be awesome

It isn't. You just lack a few levels maybe? And in general, I'm against the "I am your enemy but I'll tell you my weaknesses" style. The fact that you have doubts while fighting it is desired.What I'd rather add, is a scan spell that later permits you to decipher certain weaknesses, but not at that level of the game.

Additionally, it would be very useful if buffs gave some indication of when they were about to expire (such as fading out over the last three seconds)

Yep, I'd like to add a green bar on the effects displayed bottom-left of the character portrait telling approx how much time is left to the effect in battle. (but I won't go into that in the map mode, I think)All that will come in time.